Lubricating fluid circulating type bionic super-smooth and anti-drag surface and preparation method thereof

Abstract

The invention discloses a lubricating fluid circulation type bionic super-smooth drag reduction surface and a preparation method, and belongs to the technical field of drag reduction of ships and underwater vehicles. The bionic super-lubricity anti-drag surface comprises an asymmetric super-hydrophobic surface structure and a microcirculation flow channel communicating the upstream and the downstream of the asymmetric super-hydrophobic surface structure, and lubricating fluid directionally moves towards the downstream of the asymmetric super-hydrophobic surface structure along the asymmetric super-hydrophobic surface structure under the external shearing effect. An inlet of the microcirculation flow channel is located in the downstream of the asymmetric super-hydrophobic surface structure, an outlet of the microcirculation flow channel is located in the upstream of the asymmetric super-hydrophobic surface structure, and the outer edge of the outlet / inlet of the microcirculation flow channel has the underwater lubricating fluid dredging characteristic, so that lubricating fluid flowing to the downstream enters the microcirculation flow channel through the inlet under the pressure effect after being accumulated; and then the water flows reversely to an upstream outlet along the microcirculation flow channel, so that a repeatedly circulating flow process is completed. According to the invention, the lubricating fluid can be effectively sealed and stored to form an anti-drag and anti-fouling liquid-liquid interface, the automatic supplement and long-acting maintenance of the lubricating fluid can be realized, and the durability of the super-smooth surface in underwater anti-drag application is greatly enhanced.

Description

Technical Field

[0001] The present invention belongs to the technical field of drag reduction of ships and underwater vehicles, and in particular relates to a lubricating fluid circulation type bionic super-slip drag reduction surface and a preparation method thereof. Background Art

[0002] When ships and underwater vehicles are working, their outer surfaces are in direct contact with water over a large area. Due to the viscosity of water, a large friction resistance is generated during navigation. Especially for underwater vehicles, more than 80% of the energy consumption is used to overcome friction resistance. The resulting power loss has become a key issue limiting the speed and range of ships and underwater vehicles. At the same time, the development of efficient drag reduction technology is also conducive to energy conservation, emission reduction and environmental protection.

[0003] Inspired by the secretion and storage of mucus by the epidermis of pitcher plants and fish, researchers have developed a bionic super-slippery surface that can store lubricating fluids. The lubricating fluid sealed in the microstructure of the super-slippery surface can form a two-phase liquid-liquid interface underwater, produce velocity slip at the liquid-liquid interface and reduce the contact area between the surface and the water environment, thus having both anti-fouling and drag reduction potential. Artificially prepared super-slippery surfaces usually use water-insoluble lubricating fluids such as silicone oil or liquid alkanes to give them good pressure resistance and anti-solvent properties. Therefore, this type of surface has more stability and application potential than super-hydrophobic surfaces. However, in actual use, under the action of water flow, the lubricating fluid sealed on the super-slippery surface will still undergo shear loss, resulting in the loss of the drag reduction function of the super-slippery surface. The shear loss of lubricating fluids leads to reduced life and functional failure, which is the bottleneck currently limiting the application of super-slippery surfaces.

[0004] In response to this problem, the prior art discloses a variety of passive and active methods to enhance the stability of lubricating fluids on super-slip surfaces. For example, from the perspective of microstructure design, a spherical pit microstructure that imitates fish glandular cells is constructed on the surface, or a super-hydrophobic surface with a microporous cavity structure is formed as a substrate by adding a pore-forming agent during the coating preparation process. Such specially designed microstructures can significantly enhance the storage performance of the super-slip surface for lubricating fluids and extend the service life. Obviously, such methods cannot solve the problem of lubricating fluid loss under long-term flow shear. For this reason, the prior art also discloses super-slip surfaces and systems with active replenishment functions, such as forming a network cross-linked structure through a polymer substrate to store lubricating fluids, which can achieve automatic secretion of lubricating oil, or developing a lubricating fluid active release device based on porous materials. Although these methods can achieve the replenishment of lost lubricating fluids, they have the disadvantages of complex preparation methods, high preparation costs, and the need for additional energy consumption, which limits their scope of application.

[0005] Therefore, in order to promote the practical application of bionic super-slippery surfaces in the field of underwater drag reduction, it is urgent to develop solutions that can overcome the shear loss problem of lubricating fluids. Summary of the invention

[0006] Technical issues to be solved:

[0007] In order to avoid the shortcomings of the prior art, the present invention provides a lubricating fluid circulation type bionic super-slip drag reduction surface and a preparation method. The bionic super-slip drag reduction surface is designed with reference to the asymmetric stepped arrangement structure of the cross section of fish epidermal scales. The surface is conducive to the directional movement of the lubricating fluid to the downstream of the surface under the external shearing action; combined with the microcirculation flow channel opposite to the incoming flow direction, when the lubricating fluid is sheared and moves downstream along the surface and accumulates, the Laplace pressure difference generated by the asymmetric structure is used to drive the lubricating fluid accumulated downstream to be transported to the upstream of the super-slip surface through the bottom microcirculation flow channel, thereby realizing the circulation and recycling of the lubricating fluid. The super-slip surface of the present invention can not only effectively seal the lubricating fluid to form a drag reduction and anti-fouling liquid-liquid interface, but also realize the automatic replenishment and long-term maintenance of the lubricating fluid, which greatly enhances the durability of the super-slip surface in underwater drag reduction applications.

[0008] The technical solution of the present invention is: a lubricating fluid circulating bionic super-lubricating drag-reducing surface, including an asymmetric super-hydrophobic surface structure and a microcirculation channel connecting the upstream and downstream thereof, wherein the lubricating fluid moves directionally toward the downstream along the asymmetric super-hydrophobic surface structure under the action of external shear; the inlet of the microcirculation channel is located downstream of the asymmetric super-hydrophobic surface structure, and the outlet is located upstream of the asymmetric super-hydrophobic surface structure, and the outer edge of the inlet / outlet has underwater lubricating fluid-repelling properties, so that the lubricating fluid flowing downstream accumulates and enters the microcirculation channel through the inlet under pressure, and then flows in reverse along the microcirculation channel to the upstream outlet, completing a repeated circulation flow process.

[0009] A further technical solution of the present invention is that the upper surface of the asymmetric super-hydrophobic surface structure is an asymmetric stepped micron-scale microstructure in a periodic array along the flow direction, and the cross-section of a single microstructure unit is an asymmetric triangle.

[0010] A further technical solution of the present invention is: the design limitation conditions of the size of the single microstructure unit are:

[0011] L≤0.2×(γ1 / ρg)^0.5

[0012] L1>L2

[0013] L=L1+L2

[0014] Among them, L is the flow length of a single microstructure unit, γ1 is the surface tension of the lubricating fluid, ρ is the density of the lubricating fluid, g is the gravitational acceleration, L1 is the flow length of the flow surface of a single microstructure unit, and L2 is the flow length of the back flow surface of a single microstructure unit.

[0015] A further technical solution of the present invention is that the length of the single microstructure unit along the flow direction is 0.1 to 0.6 mm, and the height perpendicular to the flow direction is 0.1 to 0.6 mm.

[0016] A further technical solution of the present invention is: the microcirculation channel is formed by the gap between the substrate and the asymmetric super-hydrophobic surface structure; the asymmetric super-hydrophobic surface structure is semi-encapsulated at the opening on the top surface of the substrate, that is, the two side walls of the asymmetric super-hydrophobic surface structure parallel to the fluid flow direction are sealed and connected to the two side walls of the substrate, and a gap is left between the upstream / downstream and the other two side walls of the substrate; the part of the substrate located below the asymmetric super-hydrophobic surface structure is a lubricating fluid storage cavity, which connects the gaps on the upstream / downstream sides to form a microcirculation channel.

[0017] A further technical solution of the present invention is: the flow width of the microcirculation channel inlet is equal to the sum of the side wall gap and the flow length of the back flow surface of a single microstructure unit; the flow width of the microcirculation channel outlet is equal to the sum of the side wall gap and the flow length of the front flow surface of a single microstructure unit.

[0018] A further technical solution of the present invention is that the lubricating fluid is a lubricating oil that is insoluble in water and has low viscosity and surface tension.

[0019] A further technical solution of the present invention is: the upper surface of the asymmetric super-hydrophobic surface structure is a super-hydrophobic surface having underwater lubricating fluid properties; the end surface at the base opening is a super-hydrophilic surface having underwater lubricating fluid properties.

[0020] A method for preparing a lubricating fluid circulation type bionic ultra-slip drag-reducing surface, the specific steps are as follows:

[0021] Processing a mold-turning casting template; processing an asymmetric stepped structure on the inner bottom surface of the template of the box structure as a casting template for the upper surface of the asymmetric super-hydrophobic surface structure;

[0022] Placing a soluble template; using a water-soluble high molecular polymer to prepare a soluble template of a microcirculation channel, and bonding it to the center position of the flip casting template to obtain an integral mold;

[0023] pouring liquid polymer to prepare the base;

[0024] Curing, demoulding and masking spraying of super hydrophobic coating;

[0025] Fill with lubricating fluid.

[0026] A further technical solution of the present invention is: the method of curing, demoulding and masking and spraying the super-hydrophobic coating is:

[0027] The poured liquid polymer and the mold are left to stand together and heated and cured at a set temperature;

[0028] The solidified substrate is taken out from the template, immersed in hot water and ultrasonically cleaned to completely dissolve the soluble template inside the substrate;

[0029] The cleaned substrate is dried, and a nano-super hydrophobic coating is sprayed on the area with the asymmetric microstructure using a mask spraying method, while the substrate and edge areas remain smooth and have original wettability.

[0030] A further technical solution of the present invention is: the method of injecting lubricating fluid is:

[0031] The substrate with the asymmetric superhydrophobic surface structure is immersed in a lubricating fluid;

[0032] Vacuum and let it stand to ensure that the microcirculation channel and the super-hydrophobic surface microstructure are filled with lubricating fluid;

[0033] The soaked substrate is taken out and placed on oil-absorbing paper to absorb excess lubricating fluid, thereby completing the preparation of the bionic super-smooth surface.

[0034] A water surface ship hull, the bottom surface of which is provided with the lubricating fluid circulation type bionic super-slip drag reduction surface.

[0035] Working principle: In the initial state, the microcirculation channel and the super-hydrophobic surface microstructure are filled with lubricating fluid. Under the shearing action of the external flow, the lubricating fluid in the microstructure flows downstream and finally accumulates at the entrance of the downstream microcirculation channel. In this process, the asymmetric stepped microstructure can ensure the unidirectional flow of the lubricating fluid downstream, and the smooth substrate surrounding the super-hydrophobic surface forms a wettability step to prevent the loss of the lubricating fluid. Then the liquid-liquid interface at the entrance of the microcirculation channel changes from the initial straight state to a convex state, and the liquid-liquid interface at the outlet of the upstream microcirculation channel changes to a concave state. At this time, the Laplace pressure generated by the liquid-liquid interface at the entrance of the downstream microcirculation channel is greater than the Laplace pressure generated by the liquid-liquid interface at the outlet of the upstream microcirculation channel. Driven by the pressure difference, the lubricating fluid accumulated at the entrance of the downstream microcirculation channel automatically flows through the downstream microchannel, the lubricating fluid storage chamber and the upstream microchannel and then replenishes to the super-hydrophobic surface. Under the action of flow shear, the lubricating fluid upstream of the super-hydrophobic surface continues to move downstream, realizing the automatic replenishment of the lubricating fluid lost by shear.

[0036] Beneficial Effects

[0037] The beneficial effects of the present invention are:

[0038] (1) The present invention designs a lubricating fluid circulating bionic super-lubricating drag reducing surface. On the basis of the traditional super-lubricating surface sealing the lubricating fluid to form a liquid-liquid interface and underwater drag reducing function, the lubricating fluid can be automatically replenished through the circulation of the lubricating fluid on the surface and inside. The replenishment process is spontaneous and does not require additional energy consumption, thereby improving the maintenance effect of the lubricating fluid on the super-lubricating surface and the service life of the entire system.

[0039] (2) The present invention adopts an asymmetric microstructure that imitates fish scales. The size of the microstructure ensures that the lubricating fluid will not be lost due to gravity when the device is tilted or inverted. The asymmetric structure allows the lubricating fluid to flow in one direction under shearing without backflow. On the other hand, it creates a size difference between the front and rear microchannel openings, generating a Laplace pressure difference and driving the lubricating fluid to circulate.

[0040] (3) The present invention has a simple structure and high reliability, and the preparation method is economical and efficient. It can achieve rapid and large-scale preparation, which can greatly promote the application of bionic super-slippery surfaces in the field of underwater drag reduction of ships and underwater vehicles. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Schematic diagram of the structure of a lubricating fluid circulation type bionic super-slip drag reduction surface in an embodiment of the present invention, (a) a three-dimensional schematic diagram, and (b) a surface micrograph;

[0042] Figure 2a A schematic diagram of the cross-sectional structure of the present invention; in the figure, l1 is the length of the upstream and downstream microchannels, l2 and h are the length and height of the lubricating fluid storage chamber respectively;

[0043] Figure 2b Schematic diagram of the upstream microchannel structure in the present invention; in the figure, D1 is the size of the upstream microchannel mouth, and d is the width of the upstream microchannel;

[0044] Figure 2c Schematic diagram of the asymmetric stepped microstructure in the present invention; in the figure, L is the size of the stepped microstructure unit, H is the height of a single microstructure, and L1 and L2 are the front and rear sizes of the microstructure unit, respectively;

[0045] Figure 2d Schematic diagram of the downstream microchannel structure of the present invention; in the figure, D2 is the size of the downstream microchannel mouth, and d is the size of the downstream microchannel;

[0046] Figure 3 Schematic diagram of the working process of the present invention; in the figure, θ1 and θ2 are the contact angles of the liquid-liquid interface of the lubricating fluid at the mouth of the upstream microchannel and the downstream microchannel respectively;

[0047] Figure 4 Schematic diagram of the preparation steps of the present invention;

[0048] Explanation of the reference numerals: 1 - lubricating fluid 2 - downstream microchannel 3 - substrate 4 - lubricating fluid storage chamber 5 - upstream microchannel 6 - asymmetric super-hydrophobic surface structure. DETAILED DESCRIPTION

[0049] The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0050] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0051] In view of the problem in the prior art that the lubricating fluid on the bionic super-slippery surface is prone to loss under shear, and the limitations of the existing active and passive lubricating fluid maintenance and replenishment technologies, the present invention provides a lubricating fluid circulating bionic super-slippery surface, comprising a super-hydrophobic surface structure, a lubricating fluid, an upstream microchannel, a downstream microchannel, a lubricating fluid storage cavity and a substrate, wherein the upstream microchannel, the lubricating fluid storage cavity and the downstream microchannel constitute a microcirculation flow channel.

[0052] The upper surface of the super-hydrophobic surface structure has an asymmetric stepped micron-scale microstructure, and at the same time, there is a nano-scale super-hydrophobic coating on the micron-scale structure, which has underwater lubricating fluid affinity characteristics, can bind and seal the lubricating fluid underwater to form a super-slippery surface, and form a liquid-liquid interface with a drag reduction effect; upstream microchannels and downstream microchannels are formed between the upstream and downstream walls of the asymmetric super-hydrophobic surface structure and the inner wall of the substrate, and a lubricating fluid storage cavity is formed in the substrate below the super-hydrophobic surface structure; under the action of flow shear, the lubricating fluid moves downstream along the super-hydrophobic surface and accumulates at the downstream microchannel entrance; due to the super-hydrophobic microstructure The method is asymmetric, the size of the downstream microchannel mouth is smaller than that of the upstream microchannel mouth, and the lubricating fluid forms a curved liquid-liquid interface at the microchannel mouth and generates a Laplace pressure difference. The Laplace pressure difference drives the lubricating fluid accumulated downstream of the super-hydrophobic surface to pass through the downstream microchannel, the lubricating fluid storage cavity and the upstream microchannel in sequence, and finally flows out from the upstream microchannel outlet to the super-hydrophobic surface, realizing the circulation and automatic replenishment of the lubricating fluid; this method can realize the automatic replenishment of the lubricating fluid on the bionic super-slippery surface without consuming additional energy, effectively overcome the problem of lubricating fluid loss during use, and extend its service life.

[0053] The above technical solution is further described below in conjunction with the accompanying drawings:

[0054] In one embodiment, referring to Figure 1 As shown, the present embodiment is a lubricating fluid circulation type bionic super-slip drag reduction surface, comprising an asymmetric super-hydrophobic surface structure 6, a lubricating fluid 1, an upstream microchannel 5, a downstream microchannel 2, a lubricating fluid storage chamber 4 and a substrate 3. The super-hydrophobic surface structure has an asymmetric stepped periodic micron-scale microstructure similar to fish scales, a single microstructure unit cross-section is an asymmetric triangle, a single microstructure unit has a flow length L in the range of 0.1-0.6 mm, and a height H in the range of 0.1-0.6 mm.

[0055] Specifically, the asymmetric stepped micron-sized structure has a nano-sized super-hydrophobic coating, forming a micro-nano composite structure to enhance the binding effect on the lubricating fluid.

[0056] In one embodiment, referring to Figure 2c As shown, the flow length L of a single microstructure unit of the asymmetric stepped micrometer-scale structure satisfies L≤0.2×(γ1 / ρg)^0.5, where γ1 is the surface tension of the lubricating fluid, ρ is the density of the lubricating fluid, and g is the acceleration of gravity. Meeting this condition is conducive to the superhydrophobic microstructure to achieve stable retention of the lubricating fluid under the action of surface tension and enhance its stability. When the length of a single microstructure unit does not meet this condition, the gravity on the lubricating fluid stored in the microstructure is greater than the surface tension generated by the interface, and the lubricating fluid resistance cannot be effectively maintained under the condition of surface tilt or inversion, and the lubricating fluid is prone to loss.

[0057] Taking the incoming flow during use as a reference, the front length L1 of a single microstructure unit is greater than the rear length L2, satisfying L1+L2=L.

[0058] In one embodiment, the lubricating fluid is a lubricating oil that is insoluble in water and has low viscosity and surface tension, such as dimethyl silicone oil, long-chain alkanes, and electronic fluorinated liquid.

[0059] Reference Figure 2a As shown, the upstream microchannel and the downstream microchannel are respectively located upstream and downstream of the asymmetric superhydrophobic microstructure. Taking the incoming flow during use as a reference, the water flows from the upstream of the superhydrophobic surface to the downstream.

[0060] In one embodiment, referring to Figure 2b and Figure 2dAs shown, due to the existence of micron-scale microstructures with an asymmetric stepped shape, the size of the upstream microchannel orifice d + L1 is larger than the size of the downstream microchannel orifice d + L2, where d is the internal size of the upstream and downstream microchannels, and it should satisfy d < L2. Otherwise, under the action of gravity, the surface tension is less than gravity, and lubricating fluid loss is likely to occur. Refer to Figure 2a As shown, the length of the microchannel is l1.

[0061] Refer to Figure 3 As shown, the working process of the above embodiment is as follows: at the outlet of the upstream microchannel, the Laplace pressure generated by the bending of the liquid-liquid interface is P1 = 0.5 × sinθ1 × γ2 / (d + L1), and at the inlet of the downstream microchannel, the Laplace pressure generated by the bending of the liquid-liquid interface is P2 = 0.5 × sinθ2 × γ2 / (d + L2), where θ1 and θ2 are the contact angles formed by the liquid-liquid interface of water and lubricating fluid at the rear of the upstream microchannel and the orifice of the downstream microchannel, respectively, and the range is from -30° to 60°. The upwardly convex liquid-liquid interface is defined as positive, and the downwardly concave liquid-liquid interface is defined as negative. γ2 is the surface tension of the lubricating fluid under water.

[0062] Specifically, the upstream microchannel, the downstream microchannel and the lubricating fluid storage cavity are connected to form a microcirculation flow channel. The lubricating fluid storage cavity is between the superhydrophobic surface and the substrate, with a height of h, a length of l2, and a width of w.

[0063] Specifically, the substrate surrounds the superhydrophobic surface, and its upper surface is flush with the superhydrophobic surface. The upper surface is smooth and does not have superhydrophobicity.

[0064] The working process of this embodiment is as follows: in the initial state, the lubricating fluid storage cavity, the upstream microchannel, the downstream microchannel and the microstructures on the superhydrophobic surface are filled with lubricating fluid. Under the shear action of the external flow, the lubricating fluid in the microstructures flows downstream and finally accumulates at the orifice of the downstream microchannel. The liquid-liquid interface at the orifice of the downstream microchannel changes from the initial flat state to an upwardly convex state, and the liquid-liquid interface at the orifice of the upstream microchannel changes to a downwardly concave state. At this time, the Laplace pressure P2 generated by the liquid-liquid interface on the downstream microchannel is greater than the Laplace pressure P1 generated by the liquid-liquid interface at the orifice of the upstream microchannel. Under the driving action of the pressure difference, the lubricating fluid accumulated at the orifice of the downstream microchannel automatically flows through the downstream microchannel, the lubricating fluid storage cavity and the upstream microchannel and then replenishes the superhydrophobic surface. Under the action of the flow shear, the lubricating fluid upstream of the superhydrophobic surface continues to move downstream, realizing the automatic replenishment of the sheared and lost lubricating fluid. In this process, the flow rate of the lubricating fluid in the upstream and downstream microchannels and the lubricating fluid storage cavity is Q = w × d^3 × h^3 × (P2 - P1) / 12μ / (2l1 × h^3 + l2 × d^3), where μ is the viscosity of the lubricating fluid.

[0065] In one embodiment, refer to Figure 4As shown, this embodiment is a method for preparing a lubricating fluid circulation type bionic ultra-slip drag reducing surface based on a soluble template flipping method, and the specific steps are:

[0066] Step 1: Process the mold template. Use mechanical processing or laser engraving technology to process an asymmetric stepped structure at the bottom of the template, and select the characteristic parameter range of the microstructure according to the selected lubricating fluid.

[0067] Step 2: Place the soluble template. Prepare the microchannel and lubricating fluid storage cavity template using water-soluble polymers, such as maltose, polyethylene glycol or maltodextrin. Place the soluble template in the center of the mold template and fix it to the bottom of the mold template with a small amount of low-concentration polyethylene glycol solution or maltose solution.

[0068] Step 3: Pour liquid polymer. Pour the liquid polymer into the mold template to prepare the base. Epoxy resin, polydimethylsiloxane or polyurethane can be used as the base raw material, and then place it in a vacuum environment to remove gas.

[0069] Step 4: Curing and demoulding, mask spraying super hydrophobic coating. The poured liquid polymer is left to stand together with the mold, and heated at a certain temperature for a sufficient time to solidify it. Then the solidified substrate is removed from the template, placed in 60-80 degrees Celsius hot water and ultrasonically cleaned to completely dissolve the soluble template inside the substrate. The cleaned substrate is dried, and the nano super hydrophobic coating is sprayed on the microstructured area using the mask spraying method, while the substrate and edge areas remain smooth and have the original wettability.

[0070] Step 5: Infusing lubricating fluid. Soak the prepared base material in lubricating fluid, such as dimethyl silicone oil, liquid alkane, and electronic fluoride liquid, and place it in a vacuum for a period of time to ensure that the microchannels, lubricating fluid storage chambers, and super-hydrophobic surface microstructures are filled with lubricating fluid. Take out the soaked material, place it on oil-absorbing paper and let it stand to absorb excess lubricating fluid, and the preparation of the bionic super-slippery surface is completed.

[0071] In one embodiment, this example is the application of a lubricating fluid circulating bionic super-slippery drag reduction surface on the surface of a small surface vessel. The hull is a box-type structure with a relatively flat bottom and side structure. Therefore, the lubricating fluid circulating bionic super-slippery drag reduction surface of the present invention is directly adhered to the surface of the application hull in the form of a skin patch.

[0072] First, a lubricating fluid circulation type bionic super-slippery surface was prepared. The preparation steps were as shown in the attached Figure 4 As shown, the specific steps are:

[0073] Step 1: Processing the mold template. A pointed milling cutter with a tip diameter of 0.1 mm was used to process an asymmetric stepped structure at the bottom of the aluminum alloy template, where the length L of a single microstructure unit is 300 μm, the height H is 150 μm, the lengths L1 and L2 of the front and rear halves of the microstructure unit are 100 μm and 200 μm respectively, and the internal dimensions of the mold are 10 mm × 20 mm × 3 mm.

[0074] Step 2: Place a soluble template at the bottom of the mold. Use water-soluble polymer polyethylene glycol to prepare the microchannel and lubricating fluid storage cavity template, set the lubricating fluid storage cavity height h to 0.8mm, length l2 to 18mm, upstream and downstream microchannel size d to 80μm, length l1 to 1mm. Place the soluble template at the center of the mold template and fix it to the bottom of the mold template with a small amount of low-concentration polyethylene glycol solution. Apply a small amount of liquid release agent in the combined mold.

[0075] Step 3: pouring liquid polydimethylsiloxane. Mix a certain amount of polydimethylsiloxane prepolymer and curing agent in a mass ratio of 10:1, stir thoroughly, pour the liquid polymer into the mold template, and then place it in a vacuum environment to remove gas.

[0076] Step 4: Curing and demoulding, mask spraying super hydrophobic coating. The cast polydimethylsiloxane is left to stand together with the mold, and heated at a certain temperature for a sufficient time to solidify it. The solidified substrate is then taken out from the template, placed in 60-80 degrees Celsius hot water and soaked and ultrasonically cleaned to completely dissolve the soluble template inside the substrate. The cleaned substrate is dried, and the nano super hydrophobic coating is sprayed on the microstructured area using a mask spraying method, while the substrate and edge areas remain smooth and do not have super hydrophobicity.

[0077] Step 5: Infusing lubricating fluid. Soak the prepared base material in lubricating fluid. The lubricating fluid is dimethyl silicone oil with a viscosity of 10 cst. Leave it in a vacuum for a period of time to ensure that the microchannels, lubricating fluid storage chambers and super-hydrophobic surface microstructures are filled with lubricating fluid. Take out the soaked material and place it on oil-absorbing paper to absorb excess lubricating fluid. The preparation of the bionic super-slippery surface is completed.

[0078] Then, the batch-prepared bionic drag-reducing super-slippery surface is pasted and spread all over the hull surface. During the navigation of the ship, the bound liquid-liquid interface on the super-slippery surface can produce speed slip, thereby producing a drag reduction effect, thereby achieving energy conservation and emission reduction of the ship. At the same time, the present invention can realize the circulation and automatic replenishment of the lubricating fluid, thereby increasing the service life of the drag-reducing super-slippery surface.

[0079] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. A lubricating fluid circulation type bionic super-slip drag reduction surface, characterized in that: The invention comprises an asymmetric super-hydrophobic surface structure and a microcirculation channel connecting the upstream and downstream thereof. The lubricating fluid moves directionally toward the downstream along the asymmetric super-hydrophobic surface structure under the external shearing action. The inlet of the microcirculation channel is located downstream of the asymmetric super-hydrophobic surface structure, and the outlet is located upstream of the asymmetric super-hydrophobic surface structure. The outer edges of the inlet / outlet have underwater lubricating fluid repelling properties, so that the lubricating fluid flowing toward the downstream accumulates and enters the microcirculation channel through the inlet under the action of pressure, and then flows in the reverse direction along the microcirculation channel to the upstream outlet, completing the flow process of repeated cycles.

2. According to claim 1, a lubricating fluid circulation type bionic super-slip drag reduction surface is characterized by: The upper surface of the asymmetric super-hydrophobic surface structure is an asymmetric stepped micron-scale microstructure in a periodic array along the flow direction, and the cross section of a single microstructure unit is an asymmetric triangle.

3. The lubricating fluid circulation type bionic super-slip drag reduction surface according to claim 2, characterized in that: The design limitation conditions of the size of the single microstructure unit are: L≤0.2×(γ1 / ρg)^0.5 L1>L2 L=L1+L2 Among them, L is the flow length of a single microstructure unit, γ1 is the surface tension of the lubricating fluid, ρ is the density of the lubricating fluid, g is the gravitational acceleration, L1 is the flow length of the flow surface of a single microstructure unit, and L2 is the flow length of the back flow surface of a single microstructure unit.

4. The lubricating fluid circulation type bionic super-slip drag reduction surface according to claim 3, characterized in that: The microcirculation channel is formed by the gap between the substrate and the asymmetric super-hydrophobic surface structure; the asymmetric super-hydrophobic surface structure is semi-encapsulated at the opening on the top surface of the substrate, that is, the two side walls of the asymmetric super-hydrophobic surface structure parallel to the fluid flow direction are sealed and connected to the two side walls of the substrate, and a gap is left between the upstream / downstream and the other two side walls of the substrate; the part of the substrate located below the asymmetric super-hydrophobic surface structure is a lubricating fluid storage cavity, which connects the gaps on the upstream / downstream sides to form a microcirculation channel.

5. The lubricating fluid circulation type bionic super-slip drag reduction surface according to claim 4, characterized in that: The flow width of the microcirculation channel inlet is equal to the sum of the side wall gap and the flow length of the back flow surface of a single microstructure unit; the flow width of the microcirculation channel outlet is equal to the sum of the side wall gap and the flow length of the front flow surface of a single microstructure unit.

6. The lubricating fluid circulation type bionic super-slip drag reduction surface according to claim 4, characterized in that: The upper surface of the asymmetric super-hydrophobic surface structure is a super-hydrophobic surface with underwater lubricating fluid properties; the end surface at the opening of the substrate is a super-hydrophilic surface with underwater lubricating fluid properties.

7. A method for preparing a lubricating fluid circulation type bionic ultra-slip drag reducing surface according to any one of claims 1 to 6, characterized in that The specific steps are as follows: Processing a mold casting template; processing an asymmetric stepped structure on the inner bottom surface of the template of the box structure as a casting template for the upper surface of the asymmetric super-hydrophobic surface structure; Placing a soluble template; using a water-soluble high molecular polymer to prepare a soluble template of a microcirculation channel, and bonding it to the center position of the flip casting template to obtain an integral mold; pouring liquid polymer to prepare the base; Curing, demoulding and masking spraying of super hydrophobic coating; Fill with lubricating fluid.

8. The method for preparing a lubricating fluid circulation type bionic ultra-slip drag reducing surface according to claim 7, characterized in that: The method of curing, demoulding and masking and spraying super hydrophobic coating is: The poured liquid polymer and the mold are left to stand together and heated and cured at a set temperature; The solidified substrate is taken out from the template, immersed in hot water and ultrasonically cleaned to completely dissolve the soluble template inside the substrate; The cleaned substrate is dried, and a nano-super hydrophobic coating is sprayed on the area with the asymmetric microstructure using a mask spraying method, while the substrate and edge areas remain smooth and have original wettability.

9. The method for preparing a lubricating fluid circulation type bionic ultra-slip drag reducing surface according to claim 8, characterized in that: The method of injecting lubricating fluid is: The substrate with the asymmetric superhydrophobic surface structure is immersed in a lubricating fluid; Vacuum and let it stand to ensure that the microcirculation channel and the super-hydrophobic surface microstructure are filled with lubricating fluid; The soaked substrate is taken out and placed on oil-absorbing paper to absorb excess lubricating fluid, thereby completing the preparation of the bionic super-smooth surface.

10. A surface vessel, characterized in that: The bottom surface of the ship is provided with a lubricating fluid circulation type bionic super-slip drag reduction surface as described in any one of claims 1-6.

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